When I select "validate CSS" from the 'Document' dropdown menu, the 'WC3 CSS Validator' window comes up showing that it is happening, then the status changes to 'CSS validation done'. The window then stays where it is: the close button does not do anything, nor does the red X and the validation report does not come up on the browser. I then have to use the task manager to get out of it, because the HTML Editor is waiting for the validator window to close.
This happens most of the time but yesterday it actually worked a couple of times. One time I actually got a validation (actually 'not validated') report; the other times I got a screen asking me for file names & I couldn't find a way to get it to see the file on my machine.
I am not aware of doing anything different this time: what could I do wrong when it looks so easy??

What kind of internet connection do you have?

it's 120Mb/sec download, 10Mb/sec upload over fibre broadband. All my other internet applications work fine, with no stability problems.

Where are you located?

Reading, Berkshire, UK

I wonder if it's a connection issue?

I would be surprised, because I have Outlook and Firefox open at the same time and I am definitely online. This would be the only thing that has any connection problems at all. I have used the HTML validator with no problems ever. In fact I just tried them both again and they both worked - typical!

If it is a connection issue, why does it not just produce an error message and let me close the window so I can carry on with what I was doing?

If you close other apps does it seem better?

I had the same ones open when I tried it a few minutes ago and it worked as I did yesterday when it kept hanging. I may have had more windows open in Firefox today, actually! Does the validator use a massive amount of bandwidth?

You could open a support topic and put these questions in front of the CC gurus. They my be able to give you a better answer.